Coated nanotubes make biosensors

December 29, 2004/January 5, 2005

A good sensor should be able to sense extremely
small changes and should be able to transmit this information about its
environment consistently.

Researchers working to make sensors that indicate a given chemical
or biological agent after sensing only a few or even a single molecule
of that substance are turning to the minuscule tools of nanotechnology.

Researchers from the University of Illinois at Urbana-Champaign
are using carbon nanotubes to sense single molecules, and are tapping
the way carbon nanotubes give off near-infrared light in order to read
what the sensors have detected.

Carbon nanotubes are rolled-up sheets of carbon atoms that can
be narrower than 1 nanometer in diameter. A nanometer is one millionth
of a millimeter, or the span of 10 hydrogen atoms.

The sensors could eventually be used to monitor biochemical changes
in biological fluids and tissue in real time, according to the researchers.

Carbon nanotubes floresce, or emit light after absorbing light,
at a wavelength in the near infrared region. This is useful because near
infrared wavelengths are not blocked by human tissue or biological fluids;
this allows for sensors that can transmit information from inside the
body. Unlike quantum dots and organic molecules, which are also being
studied for use as biological sensors and markers, nanotubes do not lose
their ability to fluorese over time. This consistency makes it possible
to derive information from the wavelength and intensity of the fluorescence.

The researchers modified carbon nanotubes so they stick to a target
molecule; when they do so their fluorescence diminishes, which indicates
that the molecule is present. The researchers proof-of-concept system
detected glucose levels in a sample of blood.

The method could be used practically in 5 to 10 years, according
to the researchers. The work appeared in the December 12, 2004 issue of
Nature Materials.